Hagmann free-flow valve.
The Bach 42A Stradivarius Tenor Trombone with Hagmann Valve is a great choice for the player looking for a less resistant F attachment. It features the Rene Hagmann Free-Flow™ valve which eliminates the back pressure that occurs in the F attachment with traditional rotor systems. The 42A offers an open response in all registers, with it's 8.5-inch one-piece hand-hammered bell, .547-inch bore with an open wrap F attachment. It includes a deluxe case and mouthpiece.